This invention relates to a guide for a mechanical power transmission device, of the kind used in an automobile engine for valve timing, in which power is transmitted through a flexible, circulating, power transmission medium such as a chain, a belt or the like. The invention relates more specifically to a guide which limits the traveling path of the transmission medium, to prevent vibration noise, transverse vibration, and meshing failure, or to a guide which, in cooperation with a tensioner, imparts tension to the transmission medium.
FIG. 8 shows a typical timing drive of an engine E, in which an endless chain C, travels over a driving sprocket S1 and a pair of driven sprockets S2. A movable guide Ga, over which the chain C slides, cooperates with a tensioner T to impart tension to the chain. A fixed guide Gb limits the traveling path of the chain C to prevent vibration noise, transverse vibration, and meshing failure. Both guides are attached to an inner wall of the engine by attachment means P, which may be mounting bolts, pins or the like.
As shown in FIG. 9, the movable guide Ga comprises a shoe A11 for sliding contact with a chain, and a guide body A10 integrally molded with the shoe. The guide body includes a plate-receiving portion A12, which extends longitudinally along the back of the shoe A11, that is, on the side of the shoe opposite the chain-contacting side. A reinforcing plate A20, which reinforces the guide body A10, fits into a slot A12a, which is open along the length of the plate-receiving portion A12. The movable guide Ga is mounted on an inner wall of an engine by a mounting bolt P, which is inserted into a mounting hole A12b bored through the guide body A10 and a mounting hole A21 bored through the reinforcing plate A20, and in register with hole A12b when the reinforcing plate is located in the slot A12a. 
In the conventional movable guide Ga, the mounting hole A12b in the guide body A10 has the same hole diameter as the mounting hole A21 in the reinforcing plate A20. Thus, when the centers of the hole A12b and the hole A21 are shifted relative to each other by even a slight distance during assembly, either in the longitudinal direction of the guide or in the front-to-rear direction, in many cases the mounting bolt P cannot be inserted through the mounting holes. Moreover, when the mounting bolt P can be inserted through the holes, the tightness of the fit resulting from misalignment of the mounting holes can prevent the guide from pivoting smoothly on its mounting bolt.
In a high temperature environment such as encountered in an engine the guide body A10, which is composed of synthetic resin, is subject to thermal shrinkage, which can cause the guide body A10 to shift relative to the reinforcing plate. Such shifting not only impairs smooth rotation of the guide on the mounting bolt P, but also deforms the shape of the guide and reduces its strength and durability significantly.
Accordingly, among the objects of the invention are the solution of one or more of the above-mentioned problems of the prior art, and the provision of a guide for a flexible transmission medium, in which a reinforcing plate can be easily fitted into a guide body during assembly, and which can be easily mounted on bolt or mounting pin in a location such as on an inner wall of an engine.
To address the above objects the guide in accordance with the invention comprises an elongated guide body and a reinforcing plate. The guide body is composed of an elongated shoe having a front surface for sliding contact with the power transmission medium and a back side, and a plate-receiving portion extending longitudinally along the back side of said shoe and having a longitudinally extending slot open in a direction opposite to the direction in which said front surface of the shoe faces. The shoe and plate-receiving portion are integrally molded as a unit from a synthetic resin. The reinforcing plate fits into the slot. The guide body has a nearly circular, but elongated, mounting hole adjacent one end of the guide body. The mounting hole in the guide body is elongated in the front-to-back direction of the shoe. The reinforcing plate has a circular mounting hole, and the elongated mounting hole of the guide body overlaps the circular mounting hole of the reinforcing plate. An attachment means, such as a bolt or pin is inserted through the circular and elongated mounting holes, and supports the guide on an inner wall of an engine.
The plate-receiving portion has first and second ends spaced from each other along the longitudinal direction of the guide body, and, in a preferred embodiment, the guide body has a positioning guide wall at one end of its plate-receiving portion, for guiding the reinforcing plate in the front-to-back direction of the shoe during assembly of the guide, and limiting the shift of the reinforcing plate in the longitudinal direction of the guide body during operation of the guide.
The guide according to the invention may be a fixed guide for sliding contact with a chain, a belt or other circulating transmission medium, in order to prevent vibration noise, transverse vibration, meshing failure and the like by limiting the traveling path of the transmission medium. Alternatively, the guide may be a movable guide, which, in cooperation with a tensioner, imparts appropriate tension to a circulating transmission medium.
The synthetic resins of which the guide body is composed are not limited particularly, but they are preferably synthetic resins such as nylon 6, nylon 66, and all aromatic nylons referred to as xe2x80x9cengineering plastics,xe2x80x9d which have excellent wear resistance and lubricating properties, so that they are suitable to function as a shoe for sliding contact with a traveling transmission medium. The resins may be fiber-reinforced where improved strength is required.
The reinforcing plate may be composed of any suitable material which can reinforce the guide body. For example, iron-based metal such as cast iron, stainless steel or the like, non-iron metals such as aluminum, magnesium, titanium or the like, and engineering plastic having high bending rigidity and strength, and fiber-reinforced plastics or the like may be used. Further, by providing a plurality of punched holes in the reinforcing plate, distributed in the longitudinal direction of the guide, a significant reduction in the overall weight of the guide can be attained.
The attachment means for attaching the guide to an inner wall of an engine may be a mounting pin, a mounting bolt and the like. For a movable guide, the attachment means serves as a pivot at one end of the guide. Attachment means may be provided at both ends of a fixed guide. In either case, the specific shapes of the attachment means are not particularly limited.
The mounting hole in the guide body, which is nearly circular, but slightly elongated in the front-to-back direction, overlaps the circular mounting hole in the reinforcing plate. The guide body is mounted on an inner wall of an engine by an attachment means, inserted through both mounting holes. Even if a shift in the relative positions of the guide body and the reinforcing plate occurs during the mounting of the guide, an attachment means such as a mounting bolt or the like can be easily inserted and secured. The relative positions of the holes in the guide body and reinforcement plate can be adjusted in the process of mounting the guide on the attachment means.
In the case of a movable guide, when the guide body, which is composed of synthetic resin, is pivoted on a bolt or other attachment means on an inner wall of an engine, it is subject to thermal shrinkage as a result of its exposure to high temperature. The elongated mounting hole in the guide body not only absorbs the positional shift due of the guide body resulting from thermal shrinkage, thereby ensuring smooth pivoting of the guide on the attachment means, but also absorbs deformation of overall shape of the guide, and maintains the strength of the guide over a long period of time.
Since a positioning guide wall is provided on one end of the plate-receiving portion of the guide body, the reinforcing plate is guided in the front and back direction during assembly. The positioning guide wall also contributes to the restriction of the reinforcing plate against longitudinal shifting while the guide is in use.